The present invention relates to a liquid crystal driver circuit which displays data on a liquid crystal display, and more particularly to a liquid crystal driver circuit which applies a drive voltage to a liquid crystal panel at a high speed.
As described in xe2x80x9cAn 8-bit Digital Data Driver for Color TFT-LCDsxe2x80x9d, pp. 247-250, in SID DIGEST, 1996, the data driver circuit (liquid crystal driver) of a conventional liquid crystal display (LCD) buffers a liquid crystal application voltage corresponding to display data generated by a digital-to-analog converter (DAC) circuit with the use-of an output amplifier circuit before output. The output amplifier circuit, composed of a voltage follower circuit, applies a gray-scale voltage of the DAC circuit directly to the liquid crystal panel pixels to display data.
In response to an increase in the resolution and size of a liquid crystal panel, the conventional driving method is designed for reducing the charge time (horizontal period) and the liquid crystal panel load but not for quickly writing data on the liquid crystal panel. That is, the conventional method is not compatible with a high-resolution, large-sized liquid crystal panel. Today, the mainstream standard for a liquid crystal panel is XGA (1024xc3x97768 dots) and SXGA (1280xc3x971024 dots). In future, the standard for higher-resolution liquid crystal panels, such as UXGA (1600xc3x971200 dots) or QXGA (2048xc3x971536 dots), and QSXGA (2560xc3x972048 dots), will be introduced. Also, the panel size will become larger, from 13-inch or 15-inch panels, which are popular today, to 18-inch or 20-inch panels.
The horizontal period, which is the liquid crystal panel write time, is about 14 xcexcs for the resolution of XGA and about 11 xcexcs for SXGA. The horizontal period is reduced as the resolution increases, that is, about 9xcexcs for UXGA, about 7 xcexcs for QXGA, and about 5 xcexcs for QSXGA. The liquid crystal panel load also increases as the panel size increases; that is, the load of a 18-inch panel is about 1.2 times higher, and the load of a 20-inch panel is about 1.33 times higher, than that of a 15-inch panel.
Therefore, it is difficult for the conventional driver circuit to write data into a high-load liquid crystal panel in such a short charge time. The picture quality is degraded because of an insufficient write voltage.
It is an object of the present invention to provide a liquid crystal driver circuit and an LCD which quickly write data into a liquid crystal panel with a large load capacity and load resistance to display high quality pictures on a high-resolution, large-sized liquid crystal display.
To solve the above problems, there is provided in the output amplifier circuit of a liquid crystal driver circuit, means for switching between an amplifier circuit that amplifies a predetermined gray-scale voltage for output and an amplifier circuit that amplifies a predetermined gray-scale voltage by a factor of 1 for buffering and outputs it with no amplification. For a predetermined part of the horizontal period, the liquid crystal panel is driven by the amplified output and, for the rest of the period, by the buffered output.
In addition, a pre-charge control circuit is provided to check whether the gray-scale voltage is to be amplified depending upon the display data.